The present invention relates to a scanning transmission electron microscope and a method of scanning transmission electron microscopy applicable to the scanning transmission electron microscope which offers substantially the same ease of operation as that of scanning electron microscopes and which provides substantially the same degree of resolution as that of transmission electron microscopes.
A scanning transmission electron microscope (STEM) based on a conventional transmission electron microscope (TEM) is disclosed illustratively in Japanese Patent Laid-open No. 016160/1977. Japanese Patent Laid-open No. 036763/1982 discloses structures of a secondary electron detector for use with a TEM-based STEM. With TEM-based STEMs, the axial alignment of their electron lens system is accomplished conventionally using a fluorescent screen in a dark room to observe electron beam paths.
Expectations were high for the advent of scanning transmission electron microscopes (STEM) which have levels of resolution as high as those of transmission electron microscopes (TEM) and which may be operated as easily as scanning electron microscopes (SEM). The above-mentioned TEM-based STEM can be a bulky machine about 2.5 m in height to house a complicated electron lens system for imaging diffraction patterns derived from transmitted electrons. Where to install such a tall TEM-based STEM has turned out to be a problem. With the TEM-based STEM, images have often been observed by use of a fluorescent screen, which requires a dark room. Furthermore, an experienced operator""s skills and knowledge have been necessary for the alignment of the optical axis of the TEM-based STEM.
Meanwhile, the scanning transmission electron microscope (STEM) based on scanning electron microscopes (SEM) has no image-magnifying lens system. That means the alignment of an electron lens system is not available on the SEM-based STEM. In addition, the SEM-based STEM is lacking in the ease of operation in that the preparation and attachment of specimens as well as the feeding of operating instructions to the machine cannot be accomplished on a display screen.
It is therefore an object of the present invention to provide a scanning transmission electron microscope (STEM) which has a level of resolution as high as that of transmission electron microscopes (TEM) and which may be operated as easily as scanning electron microscopes (STEM).
It is another object of the invention to provide a scanning transmission electron microscope (STEM) which permits the observation of scanning transmitted images of specimens in a well-lighted room.
It is a further object of the invention to provide a scanning transmission electron microscope (STEM) allowing the optical axis of a primary electron beam to be adjusted easily for observation purposes.
It is an even further object of the invention to provide an interactive input/output device which is used in conjunction with a scanning transmission electron microscope (STEM). The interactive input/output device facilitates the observation of scanning transmitted images of specimens on the microscope.
It is a still further object of the invention to provide a method of scanning electron microscopy which is for use with a scanning transmission electron microscope (STEM). The method allows internal structures of specimens to be observed in a three-dimensional fashion.
In achieving the foregoing and other objects of the present invention, there is provided a scanning transmission electron microscope comprising: an electron source for generating a primary electron beam; an electron illuminating lens system for converging the primary electron beam from the electron source onto a specimen for illumination; an electron deflecting system for scanning the specimen with the primary electron beam emitted thereto; a scattered electron detector for detecting scattered electrons transmitted through the specimen; and an image displaying system for displaying a scanning transmission electron microscope image of the specimen using a detection signal from the scattered electron detector. This inventive structure provides effectively a scanning transmission electron microscope (STEM) based on a scanning electron microscope (SEM).
In a preferred structure according to the invention, the scanning transmission electron microscope (STEM) may further comprise a detection angle changing system for variably establishing a range of scattering angle of the scattered electrons detected by the scattered electron detector. This preferred structure enhances a contrast of a desired portion of the specimen under observation for a scanning transmitted image, thereby improving the precision of structural and component analyses of the specimen.
In another preferred structure according to the invention, the scanning transmission electron microscope (STEM) may further comprise a PC-based interactive input/output device with a display screen permitting input of conditions for operating components of the scanning transmission electron microscope. This structure renders the microscope easier to operate and thereby alleviates users"" operating chores.
In a further preferred structure according to the invention, the scanning transmission electron microscope (STEM) may further comprise a secondary electron image displaying system for displaying a secondary electron image of the specimen through detection of secondary electrons released by the specimen, and/or reflected electron image displaying means for displaying a reflected electron image of the specimen through detection of reflected electrons from the specimen. This preferred structure provides more aspects of observed information about the specimen by supplementing its scanning transmitted image with a secondary electron image and/or a reflected electron image.
In an even further preferred structure according to the invention, the electron illuminating lens system may include accelerating electrostatic lenses for accelerating the primary electron beam from the electron source, and converging lenses for converging the accelerated primary electron beam onto the specimen. The electron illuminating lens system may further include an electron source deflector for aligning an optical axis of the primary electron beam from the electron source. The electron source deflector may be constituted illustratively by a scanning deflector and by two-stage deflectors with reversal polarity which are located above and below the scanning deflector.
These and other objects, features and advantages of the invention will become more apparent upon a reading of the following description and appended drawings.